Corals in Crisis

Media coverage of the coral bleaching event that rocked reefs in 2016 has been widespread and grave. Along Australia’s Great Barrier Reef there has been concern that negative messaging may deter visitors from a major tourism site. Researchers and journalists, however, argue that as bleaching occurs more frequently in our warming world, media coverage and public awareness are crucial to conservation solutions.

Coral bleaching events are triggered by raised sea temperatures. Tiny algae called zooxanthellae live inside coral polyps and produce energy, but are ejected by heat-stressed corals. Devoid of the algae that give these coral animals their colour, the white coral skeleton is exposed and the animals begin to starve. If temperatures cool sufficiently, the algae can return and corals recover. But if heat stress persists over a long period, bleached corals can die – and it can take reefs decades to recover. El Niño episodes, when warm water spreads across the Pacific Ocean roughly once every five years, can lead to coral bleaching.

El Niño events are complex and researchers are still grappling to understand them fully. This most recent episode saw raised sea temperatures lead to bleaching on reefs worldwide, although the extent and intensity of the bleaching differed at individual sites. In 2016, Australia’s National Coral Bleaching Taskforce reported that 81% of the Great Barrier’s northernmost reefs were severely bleached and estimated that 93% of the entire reef was affected. This has been called the longest – and on the Great Barrier Reef perhaps the worst – bleaching event in history.

Observations from D’Arros Island in the Seychelles echo this disturbing trend. Dr Rainer von Brandis, scientific director at the D’Arros Research Centre, and his research team have documented the bleaching event and he estimates that between 50 and 80% of all hard corals around D’Arros and neighouring St Joseph Atoll have been lost. There is, he believes, good reason for the concern shown for other bleaching sites and that the extent of media attention is well founded. When asked about the monitoring plans for D’Arros and the possibility of salvaging the region’s corals, Von Brandis is resolute: ‘Assisting in the recovery of these corals is difficult and time-consuming, but we will monitor coral cover and recruitment into the future.’

The question of whether it is possible to recover after an event of this scale and intensity plagues researchers. In many cases, scientists are concerned that recovery in highly affected areas (like the Great Barrier’s northern reaches) is unlikely. Von Brandis is cautious about what this means for D’Arros. Like other researchers, he is keenly hopeful but must be realistic: ‘The severe bleaching event of 1998 all but wiped out the corals here. It’s taken a long time, but the reefs were recovering well until this most recent event.’ Each region will differ in terms of how badly affected its corals were and its subsequent rate of coral recruitment and recovery. Past bleaching events have shown that recovery is possible. Right now, it’s up to researchers to monitor affected reefs – and for us to wake up to the impact that warming oceans will have on reefs in the future.